Flare composition comprising dry blend of metal fuel and eutectic mixture of oxidizer salts

ABSTRACT

BINDERLESS ILLUMINATION FLARE COMPOSITIONS FORMED BY DRY BLENDING A METAL POWDER AND AN INORGANIC OXIDIZE TO FORM A MIXTURE, HEATING WHILE COMPACTING THE MIXTURE IN A CASTING UNTIL FUSION OF THE OXIDIZER OCCURS, THEN COOLING THE MIXTURE. THE PREFERRED METAL POWDERS ARE ALUMINUM, MAGNESIUM OR MAGNESIUM-ALUMINUM ALLOY AND THE OXIDIZERS ARE AN ALKALI OR AN ALKALINE EARTH METAL NITRATE AND MIXTURES THEREOF.

United States Patent FLARE COMPOSITION COMPRISING DRY BLEND OF METAL FUEL AND EUTECTIC MIXTURE OF OXIDIZER SALTS Howard W. Kruse, Ridgecrest, Calif., assignor to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Oct. 1, 1969, Ser. No. 866,069

Int. Cl. C06b 15/00 U.S. Cl. 149-41 4 Claims ABSTRACT OF THE DISCLOSURE Binderless illumination flare compositions formed by dry blending a metal powder and an inorganic oxidizer to form a mixture, heating while compacting the mixture in a casing until fusion of the oxidizer occurs, then cooling the mixture. The preferred metal powders are aluminum, magnesium or magnesium-aluminum alloy and the oxidizers are an alkali or an alkaline earth metal nitrate and mixtures thereof.

GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to binderless flare compositions and to the method of preparation.

Flare compositions now used comprise a mixture of metal powder, oxidizer, and binder which is pressed in increments into a casing under high pressure. Binder material such as resins, plastics and waxes serve to make the finely divided particles of metal and oxidizer adhere to each other and thus aid in obtaining maximum density. In addition, the binder prevents metal and oxidizer segregation so that more uniformly blended compositions can be obtained. As binder content is increased, burning rate is decreased and candlepower is reduced. Because flares contain metal fuel in excess of stoichiometric proportions, this excess metal must be vaporized and then burned by atmospheric oxygen. Compositions containing binder have less heat available for metal vaporization and therefore their eflioiency is reduced. The present invention provides a simple method for the preparation of flare compositions which give intense, long-lasting illumination.

It is therefore an object of this invention to provide a simple method for the preparation of illumination flare compositions which can be used in systems requiring bright and efficient light output. Another object is to produce a flare device which is comparatively insensitive to impact, static electricity and friction thereby making them safe for personnel to handle.

DESCRIPTION OF THE INVENTION In accordance with the present invention a dry mixture was first prepared comprising a blend of a powdered metal and a powdered inorganic oxidizer in a ratio of about 50-70 percent by weight metal and about 50-30 percent by weight inorganic oxidizer. A suitable casing, such as Micarta, anodized aluminum, etc., was substantially filled with the mixture. The casing containing the mixture was next heated to a temperature suflicient to cause fusion of the oxidizer in the mixture. Any suitable heating method can be employed such as electrical heating by induction or directly by conduction. During the time of heating compaction of the material in the casing took place. Compaction is a very important step in this process because in order to get an even burning flare the product must be of a solid, smooth texture. Compaction was achieved by several means such as vibrating during the heating period; vibrating while applying slight pressure during the heating period; heating under vacuum, while slightly vibrating and applying light pressure.

Suitable oxidizing salts for use in this invention include the alkali and alkaline earth metal nitrates and mixtures thereof. Single salts can be used, but it is generally preferred to use mixtures of the salts having fairly low melting points, such as binary or ternary mixtures, preferably melting below 230 C. Examples of suitable eutectic mixtures and their melting points include: 23.5% LiNO 16.3% NaNO -60.2% KNO (M.P. C.); 30.5% LiNO -4O% NaNO -29.5% Ca(NO (M.P. 170 C.); 55% NaNO -45% Ca(NO (M.P. 230 C.); 49% NaNO -5l% Mg('NO (M.P. 135 C.); and 49% NaNO -45.4% Mg(NO -5% Ca(NO (M.P. C.). The eutectic mixtures are prefused and ground into a powder for use in the present flare compositions.

Metals used successfully were aluminum, magnesium, magnesium-aluminum alloy, pretreated dichromated aluminum and dichromated magnesium. The metals are finely divided, or powdered, the selection of particle size depending on the metal used and the burning rate. Powdered aluminum of 5 size was used successfully. Dichromated aluminum and magnesium were easily wetted by the fused oxidizer when the dry blend was heated and thereby facilitated flame preparation appreciably.

The following examples are illustrative of this invention.

EXAMPLE I A 50:50 ratio of a prefused and ground oxidizer (50 mesh) and metal powder was dry blended. For dry mixing a blender having a capacity of 5 to 50 pounds was used. The blender was located in a well ventilated building and was operated by remote control. All equipment must be grounded and every precaution taken to prevent the accumulation of static electricity as the dust produced within the blender is hazardous if the oxidizer is of a very fine grind. After about one-half hour of mixing the composition was filled into eight 40-gram flare casings. The mixture was heated in the casings for 25 minutes at -145" C. A five-minute vibration period at the end of the heating period aided compaction. The material was cooled and elficiency checked, which was low because of inefficient combustion of the metal. The oxidizer used was a eutectic oxidizer mixture composed of a mixture of 23.5% lithium nitrate, 60.2% potassium nitrate and 16.3% sodium nitrate which has a melting point of about 120 C. The metal was 5 aluminum powder. All the flares burned smoothly and the deviation in output from flare to flare was small.

EXAMPLE II Another batch of flare composition was prepared using sodium nitrate (49%) and magnesium nitrate (51%) eutectic, and magnesium powder (Gran #17). About 65% by weight magnesium powder and about 35% by weight of the eutectic oxidizer were dry mixed and 20 g. was filled into flare casings made of Micarta. The material in the casings was heated to a temperature of 150- 1'60 C. at which the oxidizer in the mixture melts. Continuous vibration took place during the heating period of 30-35 minutes and constant pressure of about 100' p.s.i. on a ram at the top of the mixture gave good compaction. The metal was dispersed throughout the oxidizer and only a very small amount of oxidizer was forced out of the mixture. Following is the output data (average) for these flares:

Burn time (seconds) 11.9 Avg. CP (K) 89.8 Cp sec./g. (K) 31.2

EXAMPLE III A 70:30 metal to oxidizer ratio dry mixture was prepared wherein the same oxidizer described in Example II was used with Gran #18 magnesium. The mixing procedure was also the same. The mixture (35 g.) was loaded into flare casings and heated While vibrating and applying slight pressure (about 100 p.s.i.) to the mixture with a ram. Following is the output data for this composition:

Burn time (seconds) 23.0

Avg. CP (K) 29.0

CF sec./g. (K) 19.0

EXAMPLE IV Several 30-gram flares in Micarta casings were prepared using dichromated magnesium powder and the sodium nitrate-magnesium nitrate eutectic oxidizer as used in Example II. The batches were made up of 65% by weight dichromated magnesium and 35% of the eutectic oxidizer and filled into 30-gram flare casings. The material was heated to a temperature of about 150-160 C. for from 30-35 minutes while compaction took place. Compacting this batch consisted in slightly vibrating during the heating period with a light pressure of 100 p.s.i. to a ram to the material, and finally cooling until the melt solidified. The dichromated magnesium powder was wetted with great ease by the fuzed oxidizer and because of this, very coarse oxidizer can be used in the dry mixes.

The preferred oxidizer eutectic was ground only fine enough to pass a 14-mesh sieve. These flares ignited readily up to 60,000 feet as did the flares with the untreated magnesium powder. Flares made with the dichromated magnesium, however, showed a consistently slightly shorter burning time, a greater brightness, and a higher efficiency. The following table will show the results of the flares containing untreated and dichromated magnesium.

TABLE I.-0 UTP UT OF FLARES AT SIMULATED ALTITUDE [Metalz Oxidant=65z351 Flares weighing 105 grams were prepared using anodized aluminum cases to which the melt will bond. A sodium nitrate-magnesium nitrate-calcium nitrate eutec- TABLE II.-OUI]?UT DATA FOR -GRAM FLARES Burn time, see.

Melt-cast flares Gran #17 Mg.:

GP, K CP, sec./g., K

containing Average 22. 6 153 32. 9

Melt-east flares containing Gran #18 Mg Average 36. 6 91. 9 32. 2

What is claimed is:

1. An illumination flare composition comprising a dry blend of from 5070% by weight of a member selected from the group consisting of aluminum, magnesium, aluminum-magnesium alloy, dichromated magnesium, dichromated aluminum, and mixtures thereof and from 50% to 30% by weight of an inorganic oxidizer selected from the group consisting of a eutectic mixture of sodium nitrate and magnesium nitrate and a eutectic mixture of sodium nitrate, magnesium nitrate, and calcium nitrate.

2. The composition in accordance with claim 1 wherein the member is magnesium and the oxidizer is a eutectic comprising about equal parts sodium nitrate and magnesium nitrate.

3. The composition in accordance with claim 1 Wherein the member is dichromated magnesium and the oxidizer is a eutectic comprising about equal parts sodium nitrate and magnesium nitrate.

4. The composition in accordance with claim 1 Wherein the member is magnesium and the oxidizer is a eutectic comprising sodium nitrate, magnesium nitrate and calcium nitrate.

References Cited UNITED STATES PATENTS 2,033,966 3/1936 Wiley 149-43 2,035,509 3/193'6 Schladt 149-41 2,316,358 4/1943 Nickle 149-43 2,992,086 7/1961 Porter 149-42 X 3,396,060 8/1968 Piccone 149-43 X 3,490,966 1/1970 Hiltz 149-41 X 3,497,404 2/ 1970 Hiltz 149-41 X 3,664,898 5/1972 Taylor et al. 149-43 X 3,104,996 9/1963 Boddey 149-41 (Other references on following page) 5 UNITED STATES PATENTS Walsh et a1. 149-41 'Picciano et a1. 149-43 X Helliwell et a1. 149- 43 X Schladt 149-43 X Schladt 149-43 Hart et a1. 14943 X Dement 14985 X Tepper 149- 43 X 6 Douda 14943 X Douda 149-43 X Bash et a1. 149-43 X Wystrach et a1. 14943 X Hiltz 149-43 X STEPHEN J. LECHERT, 111., Primary 'Examiner US. Cl. X.R. 

